Ground-state geometries, carbon clusters

A strictly linear structure for C3 was also predicted by Kurtz and Adamowicz, who used MBPT(2) with the 6-31G basis set to study the linear carbon chains C3 to C9 [243]. In these calculations, even-n C molecules were assumed to be triplets, while odd-n clusters were assumed to have singlet ground states. By constraining the geometry to be planar and C2 symmetrical, all of these molecules converged to almost linear forms with nearly equal bond lengths that is, they all have a cumulenic bonding pattern. 

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